This invention relates in general to reel to reel web transport apparatus and more particularly to an adaptive control system for reel to reel web transport apparatus which eliminates the necessity for mechanical or vacuum web buffers; for a capstan or tachometer to meter or control web velocity; and for a tension transducer to control web tension.
Reel to reel web transport apparatus are commonly used to transport a web between supply and takup reels past a utilization device. For example, magnetic tape recorders record and reproduce audio and video signals, instrumentation signals and digital data. In the transport of magnetic tape between supply and takeup reels, past record/reproduce (read/write) heads, the tape is subjected to velocity variations such as acceleration, constant velocity and deceleration which causes tape tension variations. In order to effect interchangeability of tapes between different tape recorders and faithful recording and reproducing of information on the magnetic tape, it is desirable to maintain a controlled tension on the tape during transport. If the tape tension is too small during tape transport, the tape may slacken and be damaged by becoming entangled in the tape transport mechanisms or by being loosely wound on the takeup reel. If the tape tension is too great during tape transport, the tape may become stretched during recording or reproducing, and cause signal distortion and undesirable information degradation. It is thus desirable that a controlled tension be maintained on the tape during all phases of tape operation including loss of power to the tape drive motors.
Since the inertia of a reel of magnetic tape varies as the diameter of the tape pack decreases or increases during supply and takeup, tape tension also varies and a tape buffer or storage device has been used in order to minimize the effect of such tape tension variation. Buffer devices, such as spring loaded storage arm devices and vacuum column buffer devices, are disadvantageous because of their increased mechanical, electrical and control complexity and increased space requirements. Capstan drive tape transports are also mechanically and electrically complex.
It has also been proposed to use a web tachometer to control web velocity and tension transducers to control web tension. However, these devices are undesirable due to their mechanical and electrical complexity and their sensitivity to deterioration.
Thus, a reel-to-reel tape transport which uses separate motors for driving each reel offers several advantages over capstan drive tape transports, reel-to-reel transports which include buffer devices for tape tension and speed control, and tape transports which use tape velocity and tape tension sensors for servo control of the transport. The bufferless and capstanless reel-to-reel tape transport is simpler in mechanical structure, more space efficient, and requires fewer mechanical components. It also allows for a simpler and more efficient control system since only the reel motors need be controlled. Thus, a control system for a reel-to-reel web transport apparatus should provide controlled velocity and controlled tension of the tape over the full range of tape motion (e.g., at rest, acceleration, constant speed, and deceleration) in order to minimize recorded signal degradation caused by undertensioning or overtensioning the tape.